Dredge cutterheads are used for excavating earthen material that is underwater, such as a riverbed. One example of a dredge cutterhead is illustrated in FIG. 17. In general, a dredge cutterhead include several arms 11 that extend forward from a base ring 16 to a hub 23. The arms are equally spaced about the base ring and formed with a broad spiral about the central axis of the cutterhead. Each arm is provided with a series of spaced apart teeth 12 to dig into the ground.
In use, the cutterhead is rotated about its central axis to excavate the earthen material. To excavate the desired swath of ground the cutterhead is moved side-to-side as well as forward. On account of swells and other movement of the water, the cutterhead will also tend to move up and down, and periodically impact the bottom surface. As a result of this unique cutting action, the teeth of a dredge cutterhead experience heavy transverse as well as axial loading and heavy impact jacking loads that thrust the tooth up, down and sideways. The heavy transverse loading of the tooth is further engendered by the operator's inability to see the ground that is being excavated underneath the water. Unlike other excavators (e.g., a front end loader), the operator of a dredge cutterhead cannot effectively guide the cutterhead along a path to best suit the terrain to be excavated.
Due to the rotative digging action of the cutterhead, each tooth penetrates the ground on the order of 30 times a minute as compared to about 1 time a minute for mining teeth. As a result, the teeth experience a great amount of wear during use. It is desirable therefore for the teeth to be easily removed and installed to minimize downtime for the cutterhead. As is common with wear assemblies for excavating equipment, dredge teeth comprise a plurality of integrally connected parts so as to minimize the amount of material needing replacement, i.e., only the worn components need to be replaced.
In the example of FIG. 17, each tooth includes a base 18, an adapter 13, a point or tip 17, and a lock 29. The base 18 is cast on the arm 11 at a particular location and orientation to maximize digging. Adapter 13 includes a rear end 22 that is received in a socket 14 defined in the base, and a forwardly projecting nose 15 to hold the point 17. A removable lock 29 is provided to facilitate the required frequent replacement of the tooth points 17. The adapter is held in the socket by a large fillet weld about the circumference of the rear end 22. In other known dredge cutterheads 1, the adapter 2 is bifurcated to define a pair of legs that are configured to wrap about the arm 3 (FIG. 18). These adapters are welded directly to the arm without a base member.
Although the tooth points require the most frequent replacement in a dredge cutterhead, the adapters still wear and need periodic replacement. However, replacing even a single adapter on a dredge cutterhead is a long process. The welded adapter must first be cut off with a torch. Then, portions of the arm and base that were damaged by the removal of the adapter must be repaired and rebuilt. Finally, a new adapter is welded into place. This process typically entails 10-12 man-hours per adapter. Hence, a lengthy delay in a dredging operation is unavoidable even when replacing only a single adapter. Moreover, in view of this lengthy delay, an operator will often wait until several adapters need replacement to take the cutterhead out of operation. As a result, the actual delay in operation that usually results is longer. Indeed, with a typical cutterhead having 50-60 teeth a rebuilding process of the entire cutterhead could require more than 600 man-hours. In an effort to avoid substantial loss of dredging time, most dredging operations maintain three or four cutterheads so that the entire cutterhead can be exchanged when one or more adapter needs to be replaced, the cutterhead needs to be rebuilt, or if the cutterhead breaks. However, a cutterhead is expensive. The maintaining of extra cutterheads that are not used, but held only when the one in use is serviced is an undesirable use of resources.
In one aspect of the present invention, the adapter is mechanically attached to the arm for easy installation and removal. The adapter is held to a base on the arm solely by a mechanical construction without the need for welding the adapter. In the preferred construction, the base and adapter are formed with complementary coupling configurations to prevent release of the adapter from the base except in a release direction. A removable lock is used to prevent undesired release of the adapter from the base in the release direction. With a mechanical attachment, the adapter can be easily replaced by simply removing the lock and moving the adapter in the release direction. There is no weld to be cut, no need to repair the base and arm, and no re-application of a weld. As opposed to 10-12 man-hours for replacing a welded adapter, a mechanically attached adapter in accordance with the present invention can be changed in as little as 10 minutes. This is a dramatic improvement which not only substantially reduces downtime for the cutterhead, but can also make the elimination of an entire spare cutterhead at the dredging site possible. As a result, instead of typically needing three or four cutterheads at a dredge site, only two or three may be needed.
In a preferred construction of the present invention, the adapter includes a generally T-shaped slot that receives a complementarily-shaped tongue on the base, and an opening for receiving a lock. The lock, when inserted into the opening, opposes a wall of the base and a wall of the opening to prevent release of the tongue and slot, and thereby holds the adapter to the base.
It is common for adapters of various excavators, such as a front end loader, to be mechanically attached to the excavating bucket. For example, U.S. Pat. No. 5,653,048 discloses an adapter with a T-shaped slot that receives a T-shaped boss welded to the lip of an excavating bucket. A lock is fit within an opening in the top of the adapter to prevent loss of the adapter from the lip. A bearing surface is formed at the front end of the boss to provide axial support for the adapter. While this construction well supports an adapter on an excavating bucket, it is not well suited for use on a dredge cutterhead.
In an excavating bucket, the teeth are primarily subjected to axial loading as the bucket is driven forward through the ground. However, as discussed above, the teeth on a dredge cutterhead are subjected to heavy and frequent transverse loads due to the manner in which the cutterhead is operated. In the noted '048 patent, the adapter 4 is slid onto the boss 5 with a slight side clearance for ease of assembly. The application of a large side load L applied against the tooth point 6 tends to rotate the adapter about the received boss to the extent of the defined clearance between the parts (FIG. 16). This rotation of the adapter results in the generation of resistant forces R1-R4 and high stresses being generated through essentially “point” contacts in the corners of the assembly. Although true point contact is impossible, the term is used to identify large applications of force over a relatively small area. In particular, the application of large forces R2, R3 at “points” on the front of the base and the lock 7 place exceptionally high levels of stress on the components. Such high stress levels, in turn, cause greater wearing of the parts at these locations and a shortened usable life of the parts. The increased wearing also enlarges the clearance space, which can lead to rattling of the components during use. Such rattling of the parts further quickens wearing of the parts.
In ordinary digging, such as with a front end loader, fines become impacted between the adapter and base so that rattling is reduced or eliminated even when wearing has created large gaps between the parts. However, in a dredging operation, the water sweeps the fines in and out of the gaps, and prevents the build up of fines between the parts. Since the gaps between the parts would ordinarily remain in a dredging operation, an adapter mechanically attached to a boss on a dredge cutterhead by a known construction would continually rattle against the boss and repeatedly apply large loads in point contacts along the front and rear of the adapter. Moreover, since the fines are constantly swept into and out of the gaps between the parts with the water, the fines would actually function as a grinding compound on the parts to further exacerbate wearing of the parts. Consequently, adapters for dredging operations have not before been mechanically attached to the dredge cutterhead arms.
However, these shortcomings are overcome in the present invention so that adapters in dredging teeth can be mechanically attached to the arms. In particular, the front of the base is curved and in contact with a complementary abutment of the adapter. As a result, when side loads push the adapter in a rotative manner, the arcuate shape of the bearing surfaces enables the surfaces to remain in substantially full flush contact with each other. This full contact arrangement as opposed to a point contact greatly reduces the stress otherwise experienced in the corners of the components. Rather than having high loads applied essentially as point contacts, the loads are spread over substantially the entire bearing surface to greatly minimize the stress in the parts and, in turn, substantially lengthen the usable life of the parts.
In a preferred construction, the arcuate bearing surfaces define spherical segments to maintain substantially full contact between the bearing surfaces of the adapter and the base under both horizontal and vertical transverse loading. In addition, the rear bearing surface of the base and the front of the lock are also preferably formed with similar arcuate surfaces to likewise maintain substantially full contact between the lock and the base. Preferably, the radii of curvature for the bearing surface at the front and rear of the adapter originate from the same point.
In another aspect of the invention, a wear member for use with excavators other than dredge cutterheads could also be benefited by incorporating the curved bearing surfaces described above for the adapter.
In another aspect of the present invention, the lock is formed to tighten the connection between the base and adapter. A tightened assembly alleviates rattling and thereby lengthens the useful life of the tooth. The above-noted '048, patent discloses a lock with a threaded plug that tightens the adapter on the boss. Nevertheless, the stress and strains of digging can work to loosen even an initially tightened arrangement such that the adapter will still shift and rattle against the base resulting in increased wear, particularly with the high frequency of penetration and varied loading of teeth on a dredge cutterhead. Further, with a loosening assembly, there would be nothing in a water environment to prevent the components from rattling during use.
Therefore, in accordance with another aspect of the present invention, the lock further includes a resilient element that cooperates with an actuator to maintain a tight engagement between the adapter and base even after loads have introduced wear between the parts. The resilient element is sandwiched between a pair of rigid members. The actuator initially pulls the adapter into a tight engagement with the base and draws the rigid members together to compress the resilient element. As looseness begins to develop in the assembly due to wearing, the resilient element expands to dampen any shifting or rattling of the adapter on the base and thereby maintain a tight engagement between the two components. The rigid members also preferably have at least one stop that prevents excessive compression of the resilient element. In this way, the rigid members initially form a rigid lock that is tightly set between the adapter and the base, and which also protect the internal resilient element from premature failure on account of being overloaded.
As discussed above, the arms in a dredge cutterhead have a broad spiraling configuration. As a result, the teeth each project from the arm at a unique orientation to maximize digging. Since the teeth are mounted in different orientations on the arm, care must be taken to ensure that each adapter is properly positioned on the arm. This additional positioning procedure further lengthens the time needed to install new adapters in past cutterheads. In the example illustrated in FIG. 17, a resin is poured into the socket to harden around the first mounted adapter to thus form a recess adapted to properly orient successive adapters for the dredging operation. Nevertheless, this design still requires a careful, time-consuming procedure to initially place the adapters properly on the arm as well as the extra work of pouring and curing the resin.
As can be appreciated, since there is no guiding base in the direct welding of adapters to the arms, such as in FIG. 18, it is nearly impossible to properly position each of the adapters for maximum digging efficiency. Moreover, arms on a dredge cutter do not have a uniform configuration as they extend from the base ring to the hub. To avoid the cost and trouble of having to make a specifically shaped adapter to custom fit each designated location along the arm, the adapters are formed to have a general fit on the arm. As a result, the fit is typically loose, thus making it even more difficult to properly position the adapter for welding. Digging efficiency is therefore usually lost in the improper mounting of such teeth to a dredge cutter.
In another aspect of the present invention, the arm is formed with a plurality of spaced apart locator formations along the front edge of the arm to properly position the teeth at the desired orientations. The locator formations each have the same structural configuration, although their orientations relative to the surrounding arm contour may differ so as to properly orient each tooth for the particular location along the arm. In one aspect of the invention, a separable base member is provided with a complementary coupling formation to matingly fit with the locator formations so as to support and position the adapter properly on the arm. As a result, each base can be formed with the same shape irrespective of where along the arm it is to be mounted. Moreover, these bases are adapted to be positioned on the dredge cutterhead in an easy, accurate and quick manner. In an alternative embodiment of the invention, a weld-on adapter includes a coupling formation to match the locator formations provided on the arm so that weld-on adapters can be easily secured in proper position on the arms. As with the bases of the invention, these adapters can each be made to have the same shape and easily positioned correctly irrespective of where along the arm they are to be mounted.
Another aspect of the invention pertains to an improvement in welding parts to a base surface, such as the arm of an excavator or lip of a bucket. The welding of components to a base surface results in considerable heating of both the welded part and the base surface. As each weld bead cools, it contracts to leave a residual tensile stress along the sides of the joint, i.e., in the heat affected zone. The bottom of the joint is defined by the surface of the welded part and the base surface, which abut each other but are not welded together. These unbonded surfaces act as a gap in the union of the components, which in turn, reacts much as a crack when the welded part is loaded. As can be appreciated, loads transferred through the weld joint can produce extremely high stresses at the end of the gap (i.e., at the bottom of the weld joint). This is also at the start of the heat affected zone, which is already weakened due to the heat. As a result, any failure in the connection will often begin at this point.
To improve the strength and integrity of the welding of a part to a base surface, the bottom surface of the welded part is formed with a groove near the weld bead. With this construction, as the weld bead cools and contracts, it draws the lip of the welded part (i.e., the portion outside of the groove) outward. Now the residual stress is concentrated at the top of the groove, rather than at the end of the gap. The top of the groove has a smooth radius, which provides a much lower stress concentration factor than the sharp end of the gap. It is also formed in the parent metal of the part, which is stronger than the weld material at the end of the gap. This construction, then, greatly reduces the tendency of the weld to fail.
The use of a groove in the underside of the welded part can also ease and improve the removal of welded parts from a base surface. When cutting the welded part away from the base surface with a torch (e.g., an air arc) the user can more easily follow the groove. In this way, the contour that remains is very near the original weld prep shape, and little clean-up is required before welding on a replacement part.